Work machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery typically include one or more hydraulic systems, such as brake systems, fuel systems, or other machine systems. Each of these systems generally includes one or more hydraulic actuators that operate by selectively being filled with or drained of pressurized fluid. Valve assemblies that control the flow of hydraulic fluid to and from these actuators of the system are typically called actuating valves.
During operation of an actuation valve, the stability of the fluid supplied to the valve may affect performance characteristics of the hydraulic system. For example, if the pressure of the fluid supplied through the control valve to the hydraulic system is too low, the force exerted by a tool (i.e., a brake, a cylinder, a motor, etc.) may likewise be too low. In contrast, if the pressure of the fluid supplied through the control valve to the hydraulic system is too high, the force may also be high and even possibly damaging to components of the hydraulic system. Further, if the pressure of the fluid varies significantly, the resulting force may oscillate unpredictably. When the pressure flowing through the actuation valve to the hydraulic system is too low, too high, or varies unpredictably, the resulting performance of the hydraulic system may be less than desired.
One way to improve the performance and predictability of the hydraulic system may be to employ another type of valve called a pressure relief valve. Pressure relief valves relieve pressure surges or peaks in the hydraulic system of the work machines, thereby ensuring desired system performance, while minimizing damage to the hydraulic system and improving efficiency of the hydraulic system. Pressure relief valves also help to maintain a desired pressure by creating a restriction or blocking flow.
One example of a pressure relief valve is described in U.S. Pat. No. 6,694,859 (the '859 patent) issued to Smith on Feb. 24, 2004. The '859 patent describes a pressure relief valve including a cartridge valve element assembly movable by an electric coil assembly to proportionally control the flow of fluid between an inlet port and an outlet port. The inlet port interconnects a pressure conduit and a force control chamber. The pressure of the fluid within the force control chamber acting on the valve element assembly urges the valve element assembly against the bias of a spring to control the flow of fluid between the inlet port and the outlet port. Once the pressure of the fluid within the force control chamber reaches a level sufficiently high, a force is created sufficient to overcome the force of the spring member and the valve element assembly moves in a direction to interconnect the force control chamber with the outlet port, thereby reducing the pressure in the force control chamber and the pressure conduit.
Although the system of the '859 patent may maintain a particular pressure within a hydraulic system by selectively relieving excessive pressures, the '859 patent can only be used as an add-on component. In particular, the system of the '859 patent does not also provide for controlled fluid to and/or from a hydraulic actuator. As an add-on system, the separate pressure relief valve increases cost, complexity, and unreliability.
The disclosed system is directed to overcoming one or more of the problems set forth above.